Wouldn't that be manslaughter?
Manslaughter is generally considered 3rd degree murder but the actual charge varies by state.
10 years is on the lower end of sentencing but its not unheard of. Vehicular manslaughter usually only means big prison sentences when the driver is intoxicated. Otherwise it’ll vary from 1-10 years per count based on circumstances.
Assuming the guy had a clean record and a decent lawyer, they probably offered a favorable sentence in exchange for a guilty plea. 10 years isn’t nothing, that kids life is fucked regardless.